Networks, in particular access networks of 5G mobile communication networks require stringent constraints for time and frequency. The integration of legacy compatibility to common public radio interface CPRI into Ethernet-based access networks is challenging and requires suitable scheduling mechanisms.
There are several different conventional approaches for mitigating packet delay variations within a network. A possible approach is to use boundary clocks to mitigate a packet delay variation caused by other interfering synchronization packets by partitioning a large network into network segments. Using transparent clocks mitigates variation induced by the residence time of a synchronization packet within a network bridge device by performing additional input and output timestamping. This conventional mechanism is also known as delay equalization. A disadvantage of the packet-based synchronization approaches like IEEE 1588 is that they are sensitive to packet delay variation and packet delay asymmetry caused by congestion or other reasons. For instance, the achievable precision for IEEE 1588v2 phase and time alignment is usually below 1 μs, if transparent clock mechanisms are applied. For instance, with Cisco Nexus 3000 switches a phase and time alignment below 500 ns can be reached. Further, IEEE 802.1AS can achieve an accuracy for phase and time synchronization below 500 ns.
Another conventional approach for mitigating packet delay variation is the application of available quality of service means. An example for such a quality of service means is the prioritizing of time synchronization packets and a combination of priority-based scheduling and frame pre-emption as specified by IEEE 802.1Q. Using solely priority-based scheduling can be sufficient to fulfil the requirements in some use cases. Using a combination of quality of service means like priority-based scheduling, frame pre-emption as well as using small packet sizes with not more than 300 Byte can achieve a delay variation of about 1.3 μs in smaller networks having for instance two to three hops and less than 20 network nodes. However, there are many real-word scenarios with bigger networks having a higher number of network nodes and comprising other topologies where the use of priority-based scheduling is not sufficient.
In a further possible conventional approach, the synchronization messages within the network are averaged. This means a mean value is calculated to balance packet delay variation of the synchronization packets. The averaging of synchronization messages or synchronization packages is implementable with limited effort; however, this conventional approach requires a high amount of samples to achieve low variation making this mechanism inefficient for larger networks.
A further conventional approach is the use of ranging mechanisms wherein algorithms are used to filter or select the synchronization packets which experience a minimum packet delay within an observed time window. However, this conventional mechanism works typically only for low data loads.
Another conventional approach is the calibration by external means like the Assisted Partial Timing Support APTS. The Assisted Partial Timing Support APTS uses an additional GPS (Global Positioning System) receiver at a remote radio head RRH or radio base station to perform compensation in a network where not all network elements or network nodes are time-synchronized. A pure GPS based compensation provides a typical accuracy of +−100 ns and in best cases +−50 ns. Assisted GPS can reach even higher precision. However, this approach has the significant disadvantage of being dependent on an existing GPS system.
Accordingly, there does not exist any packet-based solution for mitigating packet delay variation which can reach stringent timing requirements without drawbacks or limitations.
Accordingly, there is a need to provide a method for scheduling a transmission of packets within a network which allows to mitigate packet delay variation and which fulfils the stringent timing requirements of access networks, in particular access networks of 5G mobile communication networks.